Recently, computerization has been remarkably promoted and improved. Displays are one of essential items for the computerization, and are being used for a variety of devices such as television sets (TV), word processors, personal computers, analyzers, game machines, and vehicle-mounted monitors. Further, such displays have been extensively enlarged.
Electromagnetic waves radiated from electric and electronic devices have become one of serious social problems. Such electromagnetic waves tend to reach adjacent devices as noise or erroneously operate them. As more electric and electronic devices are used and computers are used to control such electric and electronic devices, electromagnetic wave-related problems increase and inevitably become more serious and unpredictable. Further, it is pointed out that electromagnetic waves result in health hazard. There have been controls on such problems in Europe and the United States of America. In Japan, manufacturers' organizations exercise voluntary restriction against hazards caused by electromagnetic waves.
Generally, the following measures have been taken in order to shield electromagnetic waves, e.g. cabinets or containers are made of metals or highly conductive material or metal plates are inserted between circuit boards, and cables are covered by metal foil.
However, the foregoing measures tend to adversely affect the most important feature, i.e. visibility of images on the display. In other words, shield films should not have the ability to shield electromagnetic waves but also be transparent in order to assure the image visibility.
Japanese Patent Laid-Open Publication No. Hei 10-041,682 describes an electromagnetic wave shield film filter in order to overcome the foregoing problems. In the electromagnetic film shield filter, a transparent plastic film and a conductor such as copper foil are bonded using an adhesive, if necessary, and a geometric pattern is chemically etched on the conductor. The electromagnetic wave shield filter reflects and absorbs electromagnetic waves from a display (i.e. a device) via the conductor.
Most of the electromagnetic waves from the display are reflected by the conductor while non-reflected electromagnetic waves are absorbed as electric energy and removed via an earth portion surrounding the electromagnetic wave shield filter. Generally, the earth portion is in the shape of a strip, is approximately 5 mm to 15 mm wide, and makes the conductor and a display cabinet conductive.
The electromagnetic wave shield filter is laminated with a glass plate, a plastic plate or the like, as the transparent base (e.g. a transparent plastic film) of the filter being contact with the plates or the like, and forms a front plate of the display. The front plate is integral with a cabinet in which the display body is housed. Alternatively, the electromagnetic wave shield filter may be integral with the display cabinet, or may be attached to the display body. The earth portion of the electromagnetic wave shield filter is bonded to the earth portion of the display.
The following problems seem to be present in the foregoing electromagnetic wave shield filter.
The electromagnetic wave shield filter comprises the conductor and the earth portion mounted on the transparent base as described above. The conductor and the earth portion are made of conductive materials such as metal foil while the transparent base is made of plastics, glass or the like. The transparent base and conductive materials have different coefficients of thermal expansion or deformation, which would crease the earth portion where the transparent base and the conductor of the shape of a strip overlap.
In the foregoing case, it is very difficult to smoothly and uniformly bond the conductor and the earth portion on the transparent base. Air bubbles are sometimes present between the transparent base and the conductor and between the transparent base and the earth portion, which causes non-uniform or insufficient bonding. To overcome this problem, it is conceivable to use a very strong adhesive, which might put a limit on productivity or adversely affect mass productivity. Further, if the electromagnetic wave shield filter is directly integrated to a display cabinet or to a display body, it is also very difficult to bond the transparent base and conductive members smoothly and reliably. Air bubbles may be present between the transparent base and the conductive members, which will cause partial contact or bonding thereof. Some measures should be taken in order to overcome the foregoing problems, which would adversely affect the mass productivity.
Insufficient bonding between the earth portion and the display cabinet or the display would prevent them from being electrically and reliably connected. This will reduce electromagnetic wave shielding performance and damage the display body.